A Raymond man in custody in Fresno County on federal bomb-making charges died late last month, authorities confirmed Wednesday.

Richard Wilson Key Jr., 37, died May 26 at Community Regional Medical Center in Fresno, the Fresno County Coroner’s Office confirmed.

Key, a U.S. Army Corps of Engineers employee, was indicted May 22 on a charge of planting pipe bombs at the Crossroads Christian School in Madera on May 4 and a Chowchilla Shell gas station on March 28, according to the FBI.

According to federal court records, Key was scheduled for arraignment the day after his indictment was handed down, but the May 23 hearing was continued after Judge Stanley A. Boone learned Key had “injured himself and (was) in the hospital.”

U.S. Marshals Service officials informed the court May 27 that Key “passed away this weekend while in custody at the hospital,” court records state.

It was unclear Wednesday exactly what occurred that led to Key’s death. Key’s family did not comment Wednesday.

Key was still listed Wednesday as an inmate in custody at the Fresno County Jail. The coroner’s office confirmed an investigation is underway by the Fresno County Sheriff’s Department.

Key was arrested May 8 in connection with the two planted explosives. Neither suspected pipe bomb caused any injuries and both were safely defused. Investigators found a third suspected pipe bomb when they arrested Key, the FBI said.

According to a criminal complaint filed in U.S. District Court in Fresno, the first pipe bomb was found March 28 on the ground between two large trash bins at the Shell gas station in the 100 block of North Chowchilla Boulevard.

“Written on the top of one of the caps in black pen were the words: ‘Pull to open’ and a smiley face was drawn on the bottom of the cap,” the complaint says. “The writing ... demonstrated that this bomb was manufactured for the purpose of killing or seriously injuring an unsuspecting victim.”

Children at a private religious grade school found a similar device May 4 on property owned by Grace Community Church, the FBI said.